Hi, Couple nights ago I bought a used Stihl FS85 trimmer off of Craigs List. I thought it was a real deal, and planned to use it as either a backup but now kind of need it as a brush cutter. Maybe I'm missing something but it seems a part is needed for the shaft ... the autocut 25-2 head I bought for it won't fasten on -- there doesn't seem to be enough of an output shaft. Can anyone tell me what part I need please? I attached pics if anyone can give me a hint I would appreciate it! Thanks much, L.